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Date: Thu, 18 Oct 2012 08:14:51 +0200
From: Michal Hocko <mhocko@suse.cz>
To: David Rientjes <rientjes@google.com>
Cc: Glauber Costa <glommer@parallels.com>, linux-mm@kvack.org,
        cgroups@vger.kernel.org, Mel Gorman <mgorman@suse.de>,
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        Pekka Enberg <penberg@cs.helsinki.fi>,
        Suleiman Souhlal <suleiman@google.com>
Subject: Re: [PATCH v5 09/14] memcg: kmem accounting lifecycle management
Message-ID: <20121018061451.GA21277@dhcp22.suse.cz>
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On Wed 17-10-12 16:28:38, David Rientjes wrote:
> On Tue, 16 Oct 2012, Glauber Costa wrote:
[...]
> > +
> > +static void memcg_kmem_mark_dead(struct mem_cgroup *memcg)
> > +{
> > +	if (test_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_accounted))
> > +		set_bit(KMEM_ACCOUNTED_DEAD, &memcg->kmem_accounted);
> > +}
> 
> The set_bit() doesn't happen atomically with the test_bit(), what 
> synchronization is required for this?

The group has to be active in order to become dead so the ordering is
natural and you do not need to test&set atomicaly. Also once a group
becomes active it is always marked that way until it goes away.
-- 
Michal Hocko
SUSE Labs